178 THE PHYSIOLOGY OF REPRODUCTION 



force is located a little behind the head. The head itself 

 does not appear to be concerned in the movements of 

 locomotion. 



The movements of spermatozoa have probably been studied 

 most closely in Insecta and Echinodermata. Buller ^ says that 

 the sperms of the Echinoidea in a drop of sea-water (or the 

 medium in which they are normally discharged) swim spirally, 

 so long as they do not come into contact with the surface. The 

 spirals may be so steep that the sperms appear to move almost 

 in a straight hne, in which case progression across the field of 

 the microscope is relatively rapid. In other cases the incline 

 of the spiral is so shght that the spermatozoa swim almost in 

 circles, and consequently move forward across the microscopic 

 field with great slowness. Every gradation between these two 

 extremes was observed, but the more active sperms generally 

 swam in the steeper spirals. 



Dewitz ^ has shown that when the spermatozoa of the cock- 

 roach are put into 0'6 per cent, solution of sodium chloride, and 

 placed between two surfaces, such as those of a shde and a 

 cover-glass, they collect after a short time, partly upon the 

 upper surface of the slide and partly upon the lower surface of 

 the cover-glass. In these positions they describe circles with 

 their tails, the rotation being invariably counter-clockwise. 

 The bulk of the hquid remains free from spermatozoa, the latter 

 adhering to the glass surfaces after having once reached them. 

 If a ball be placed in the fluid, its surface is soon sought by the 

 spermatozoa.^ Verworn has described this phenomenon under 

 the name of " barotaxis," and states that it is caused by pressure 

 acting unequally on different sides of the spermatozoon. It is 

 said to be of great importance in the process of fertihsation, 

 and probably assists the spermatozoon in entering the micropyle 



• Buller, " Is Chemotaxis a Factor in the Fertilisation o£ the Eggs of 

 Animals ? " Quar. Jovr. Micr. Science, vol. xlvi., 1902. 



^ Dewitz, " Ueber Gesetznaassigkeit in der Ortsveranderung der Sper- 

 matozoen," &c., Pfiiiger^s Archiv, vol. xxxviii., 1886. Eotation by spermatozoa 

 seems to have been recorded first by Eimer, " Untersuchungen Uber den 

 Ban und die Bewegung der Sameufaden," Verhand d. Phys. Med. Oesel. zur 

 Wurzhurg, vol. vi., 1874. 



' Ballowitz, "Untersuchungen iiber die Struktur der Spermatozoen," 

 &c., Zeitschr.f. Zool, vol. i., 1890. 



